Thermal power plant
The Kriel power station is located between the towns of Kriel and Ogies in Mpumalanga, South Africa. The planning, design and construction of the plant were started in the early 1970s and commissioning was completed in 1979. The plant was considered the biggest coal-fired station in the southern hemisphere at the time.
Operated by Eskom, the Kriel power station has a gross installed capacity of 3GW. The Kriel power station built the foundation for the development of other large capacity power plants in the region, including Matla, Duvha, Kendal, Lethabo and Matimba.
The Kriel power station is installed with six Steinmüller-Benson boilers and six Brown-Boveri reaction impulse blading-type turbines.
Pulverised coal is fed to the boiler burners through a stream of hot air, then burnt and blown into the furnace at a temperature of approximately 1,275°C. The tubing in the boiler walls contains feed water that absorbs the heat from the burning coal and is converted into steam.
The steam passes through superheaters, where its temperature rises and is then transferred through pipes into the high-pressure turbine. The turbine rotor spins to generate electricity.
The exhaust steam from the turbine is returned to re-heater of the boiler, where the steam temperature rises again but at a lower pressure. The steam is then transferred to the intermediate-pressure turbine and the exhaust steam passes into the two low-pressure turbines.
The Kriel power station is equipped with condensers, extraction pumps, condensate polishing plant, feed-heating plant, de-aerator, boiler feed pumps, high-pressure feed heaters and cooling towers.
The plant also contains a water treatment plant, a circulating water system and an electrodialysis reversal plant (EDR), which is the largest of its kind in the southern hemisphere.
Kriel has been using the Vaal river water since 1983. The water contains four times higher level of dissolved salts than the Usutu water, which the plant was using before 1983.
The existing demineralising water plant was unable to treat the water from the Vaal river, so the water had to be retreated before being transferred to the demineralising plant.
Hence, the EDR water treatment plant was constructed to address the issue.
Fully mechanised Amcoal’s Kriel colliery is a direct Kriel power station coal supplier. The coal is transported through overland conveyor belts from the mine to coal staithes.
It is then fed into the underground conveyors that transfer the coal into the seven boiler bunkers located 37m above-the-ground level in the boiler house.
The coal is fed into the pulverised-fuel mills with the help of feeders, where it is ground to thin powder by steel balls running in a circular motion. The pulverised coal is transported to the boilers through primary air.
In January 2006, GE Consumer and Industrial was contracted for the replacement of the equipment originally installed at the Kriel power station to increase the lifespan of the station by approximately 25 years. According to the contract, GE was also tasked to replace the low-voltage switchgear with new technology.
Eskom awarded Alstom a contract to retrofit the low-pressure steam turbines at the Kriel power station in December 2012. The retrofit on the station’s six 500MW units included the supply, installation, testing and commissioning of 12 low-pressure turbine inner modules and the supply of two low-pressure rotors.
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